1. Field of the Invention
The invention is directed to an adjustable damping valve device having a first valve and an emergency operation valve operated by a shared solenoid.
2. Description of the Related Art
Depending upon the design principle, a damping valve that is adjustable by a magnetic force adopts a particularly soft or a particularly hard damping force characteristic in a currentless state. This effect is produced at least by a spring force against which the magnetic force must act. In case of an outage of the magnetic force, e.g., due to cable breakage, the spring force displaces a valve body into an end position. Assuming that a high damping force also represents high safety reserves for a chassis of a vehicle, then the basic operating principle is advantageous, since the safety device for the adjustable damping valve already exists in practice without further expenditure.
It is known from EP 0 561 404 B1 or DE 39 17 064 A1 that it is not necessarily the hardest damping force adjustment that is sought as an emergency operation characteristic, but rather a moderate damping force characteristic. EP 0 561 404 B1, FIG. 2 shows an adjustable damping valve device that comprises a pilot valve device and a main valve device. The damping force of the damping valve device is adjusted through the flow-off of damping medium from a control space of the main valve.
The pilot valve device comprises a pilot control valve and an emergency operation valve. The two valves are arranged in series with respect to the flow path of the damping medium from the control space (FIG. 2). Even with a small energizing current, the emergency operation valve (529a) opens and completely releases the flow-off (26i). Only cross section 26i works in the emergency operation position and therefore determines, e.g., a medium damping force adjustment.
In a variant according to FIG. 6 in EP 0561 404 B1, the pilot valve device likewise comprises an emergency operation valve hydraulically connected in parallel to the pilot valve. This poses the problem that a malfunction of the emergency operation valve also affects the damping force adjustment of the pilot valve.
The construction principles in both FIG. 2 and FIG. 6 present the difficulty that the axially movable valve body of the pilot valve and the emergency operation valve body are in direct contact, and the emergency operation valve carries out a displacing movement on the valve body of the pilot valve starting from the emergency operation position into the normal operation position.
The two valve bodies of the pilot valve device must be able to move very smoothly relative to one another. This results in small annular gaps which, on the one hand, bring about internal leakage that influences the damping force adjustment and, on the other hand, impair the guiding of the valve body relative to the solenoid.
These difficulties can be overcome, but the expenditure on fabrication required for this purpose adds to production costs.